This invention relates to the continuous removal of ethylene oxide from a gaseous stream and in particular, relates to a system for removal of ethylene oxide from the stream effluent of an ethylene oxide sterilization unit.
The use of ethylene oxide as a gas sterilization medium is well known and has been widely employed for sterilizing reusable medical devices in small portable sterilizing units as well as in the manufacture of disposable, packaged, medical goods such as sutures, surgical sponges and the like which utilize large continuous or semicontinuous sterilizing chambers. In the case of small, portable sterilization units as well as for the large commercial units, a volume of ethylene oxide is introduced either alone or in combination with a diluent gas into a chamber containing the objects to be sterilized. The chamber is sealed and held in this condition until the sterilization process is completed. Thereafter, the ethylene oxide containing gas is discharged from the chamber and generally, the chamber is purged of residual gas.
Great care must be taken in disposing of the vented ethylene oxide containing gases as such gases are extremely toxic. Accordingly, in the case of small portable sterilizers, it has been suggested in U.S. Pat. No. 4,112,054 that the discharged gas from the sterilizer be charged into a vessel containing an aqueous acid solution. The vessel accepts the full discharge from the sterilizer and is sealed. The gas charged to the vessel dissolves into the liquid solution and, to a degree, reacts to form ethylene glycol and/or polyethylene glycol. After sufficient time has passed for the dissolution and reaction to take place, the liquid containing the dissolved ethylene oxide and reaction products is removed from the vessel and discharged in a sewer system. The now essentially ethylene oxide free carrier gases are vented from the vessel.
This batch operation works well for small portable sterilizing units provided that care is taken in controlling the temperature rise within the closed vessel after it has been charged with the discharge gases from the sterilizer. This temperature rise is a result of the exothermic reaction which takes place as the ethylene oxide is converted and dissolved and, since the system is closed, heat generated by the reaction acts to raise the temperature of the system. The adverse effect of this temperature rise is to shift the vapor-liquid equilibrium concentration of the ethylene oxide so as to cause a greater concentration of ethylene oxide in the vapor phase, i.e., the gases vented from the vessel. To counteract this tendency for rising temperatures, a large quantity of aqueous solution is provided in the vessel, as compared to the quantity of gas charged. This large quantity of liquid then acts as a heat sink to maintain the temperature rise within acceptable limits.
While the above-described batch-like system is said to be practical in connection with the use of small, portable, sterilization units, it is quite clear that such a system is totally impractical when applied to large commercial units. In the latter case, extremely large quantities of gas are to be vented from the sterilizer on a continuous or semicontinuous basis and if the aforementioned batch-like system were to be used, extremely large pressure vessels would be required. Moreover, an enormous quantity of aqueous acid solution would be required to preclude an impermissable temperature rise during the course of the exothermic reaction.
Accordingly, there is a need for a system for handling the vented ethylene oxide containing gas streams in a commercially practical manner.